Offshore gas treatment and/or CO2 capture units using amine wash processes comprise liquid or gaseous fluid absorption and regeneration columns. These columns operate under counter-current or co-current gas/liquid flow conditions and they are installed on vessels, floating barges or offshore platforms, of FPSO (Floating Production, Storage and Offloading) type or of FLNG (Floating Liquefied Natural Gas) type for example. Floating barges also comprise distillation columns or dehydration columns.
The columns used in these offshore gas treatment and/or CO2 capture and/or distillation and/or dehydration units are generally based on the principle of a material and/or heat exchange between the gas and the fluid that circulate in the columns. Contacting columns generally consist of a cylindrical enclosure provided with internal contacting elements promoting exchange between the fluids. The contacting elements (contactor) that increase the contact surface area can be structured packings, random packings or trays. FIG. 1 shows a particular case of a gas treatment column (1) equipped with a distributor tray at the column top. In this example, the gas (G) and the liquid (L) circulate in a counter-current flow. Conventionally, this gas treatment column (1) comprises several sections 3 filled by a contactor, and a distributor tray 2 is arranged above each contactor 3. The gas/liquid contactor contacts gas G with liquid L so as to allow exchanges.
The gas/liquid contact columns considered are placed on floating structures, of vessel, platform or barge type for example, sensitive to the wave motion. The equipments installed on these units, notably the gas/liquid distributor trays and the contactors, therefore undergo wave motions up to six degrees of freedom (yaw, pitch, roll, heave, sway, thrust).
By way of indicative information, the angle associated with the combination of the pitch and roll oscillations is of the order of +/−5° with a period ranging from 15 to 20 s. The orders of magnitude of the longitudinal, transverse and vertical accelerations encountered in the column respectively range between 0.24/0.76/0.25 m/s2 6 m above the deck where the column is arranged and 0.33/1.28/0.33 m/s2 50 m above the deck. Under such conditions, the operation of conventional contact columns can be greatly disturbed. Indeed, under the effect of the wave motion, the inclination of the column degrades the homogeneity of the phase distribution in the column section.
If it is not controlled, this poor distribution in the packing bed can substantially degrade the performances of the contact column. In order to avoid this type of problem, various suitable structured packing piles have been developed.
For example, patent application U.S. Pat. No. 5,486,318 discloses contactor embodiments with partitioning of the packing section. In a first embodiment, the packing section is partitioned by perforated walls. The column is thus made up of several compartments equipped with structured packings. In a second embodiment, each packing section is perpendicularly adjacent to the other section, thus the total section of the column is made up of a multiplicity of structured packing sections.
Furthermore, patent application U.S. Pat. No. 5,984,282 discloses a contactor embodiment where, in the axial direction of the column, the structured packing elements are arranged in such a way that each packing section assembly surrounds a central packing section body. However, this implementation is complex.
Besides, patent applications U.S. Pat. Nos. 7,559,539 and 7,559,540 disclose contactor embodiments where the packing bed consists of two packing types with different geometric areas. The packing beds having different areas can be superimposed in the axial direction of the column or in the radial direction according to the patent. In patent applications U.S. Pat. Nos. 7,559,539 and 7,559,540, the section of the column is not split into several packing sections, therefore, under the action of the three-dimensional wave motion, the embodiments do not allow to prevent lateral displacement of the liquid in all directions. These embodiments do therefore not provide good distribution of the liquid and vapour phases in an offshore environment.
These solutions are generally implemented by means of structured packings that afford the advantage of being less sensitive to the marine environment than random packings. Now, random packings also involve interesting qualities in terms of transfer efficiency, low pressure drop and ease of installation.
The present invention allows to overcome the drawback related to the use of random packings in offshore contact columns. The contactor according to the invention comprises a random packing arrangement in several compartments, which allows to provide good distribution homogeneity in the contact column and thus to benefit from the advantages provided by random packings in a marine environment. The compartments are delimited by walls consisting of perforated plates or structured packings. The invention then allows to ensure smooth operation of the column, notably in case of inclination of the column, whatever the direction of inclination thereof.